Ultrasonic waves may be used to transfer power wirelessly between ultrasonic transducers. Multiple ultrasonic transducers may be used to transmit power to multiple ultrasonic transducers. The amount of usable power generated by the receiving ultrasonic transducers, and amount of rectification needed, may be affected by the spatial variations in phase among the ultrasonic waves as they are received at the receiving transducers. The spatial variations in phase may be due to the orientation of the receiving ultrasonic transducers relative to the transmitting ultrasonic transducers, variations in phase among the ultrasonic waves output by the transmitting ultrasonic transducers, and interference between the ultrasonic waves output by the transmitting ultrasonic transducers.